Can Power Attack be used with light weapons?

Question

I've searched the web for this but haven't found a conclusive answer. Most answers indicated that it is possible. So, Can I use Power Attack with light weapons? If it can be done, why does this feat exist;

Piranha Strike (Combat)

You make a combination of quick strikes, sacrificing accuracy for multiple, minor wounds that prove exceptionally deadly.

Prerequisites: Weapon Finesse, base attack bonus +1.

Benefit: When wielding a light weapon, you can choose to take a -1 penalty on all melee attack rolls and combat maneuver checks to gain a +2 bonus on all melee damage rolls. This bonus to damage is halved (-50%) if you are making an attack with an off-hand weapon or secondary natural weapon. When your base attack bonus reaches +4, and for every 4 points thereafter, the penalty increases by -1 and the bonus on damage rolls increases by +2. You must choose to use this feat before the attack roll, and its effects last until your next turn. The bonus damage does not apply to touch attacks or effects that do not deal hit point damage. This feat cannot be used in conjunction with the Power Attack feat.

Answer 1

Yes.

Check the prerequisites. Power Attack needs a Strength 13, while Piranha Strike needs Weapon Finess, which is interesting only if your Dex is greater than you Str, so we can deduce that the latter is intended for Dexterity-oriented characters, the fluff text incidentally says one using Piranha Strike provokes "multiple, minor wounds".

For a more complete answer, Power Attack doesn't say anything about light weapons, but it does say that you can use this feat with a natural weapon, and natural weapons are considered light weapons.

Besides, if you couldn't use Power Attack with a light weapon, the description of the Piranha Strike feat wouldn't explicitly tell that

This feat cannot be used in conjunction with the Power Attack feat

Answer 2

As you saw on the forums and as Trajan demonstrated, Power Attack can be used with light weapons in Pathfinder.
So, why does Piranha Strike exists?

I'd say it's a slightly worse version of Power Attack that can be taken with different prerequisites.

I'm not familiar enough with Pathfinder to tell but I also guess the two feats are the prerequisite for different sets of other Feats or Prestige Classes.